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Frequently asked Questions- Motors

What type of linear bearings are needed?

Linear bearings are the components that allow the machine to glide along the X, Y , and Z axis. It is essential that they have three critical properties:
  - straightness
  - frictionless
   -wearabilty

Of course, like many things, there are a variety of mechanisms to achieve the above three qualities.

Large expensive machines generally use a profiled steel guideway and recirculating ball bearing "pillow blocks" for the linear bearing. The profiled guideway is usually a heat treated and precision ground piece of steel that has grooves running down two sides. The grooves have a "gothic arch" shape so that ball bearings will contact the groove at two points  thus providing low friction. The pillow blocks, again hardened and precision ground, have ball bearings that are continously recirculating as the pillow block transits the guideway.

As you can iumagine in a woodworking environment, the ball bearings can get clogged with sawdust if the seal is not perfect. This system is very expensive generally. In an attempt to get the cost down, many lower end machines have an extremely small pillow block with very tiny ball bearins (<3/16" diameter) which compunds the problem.

Many cheap machines employ a V Guidewheel which rides along a steel track. Oftentimes the track is not a hardened and ground steel surface which will present accuracy and wear problems.

A good compromise between the two systems is a gothic arch guidewheel which ride along a hardened and ground round linear shafting. The guidewheels have a gothic arch on the outside (just like the more expensive recirculating system) and have a double row angular contact recirculating ball bearings on the inside for high stiffness.

The advantage of a profiled guidewheel system is cost and also that they can run a very high speeds becasue of the gothic arch shape. Also, the bearing itself is completely sealed and can run through quite a bit of sawdust without getting the least bit clogged up.

One of the guidewheels can be replaced at low cost, unlike the recirculating system where an entire pillow black muyst be replaced.

If coupled with a precision hardened and ground linear shafting, this system is a very good one for a CNC router.

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